DESCRIPTION (Applicant's abstract): How aerobic exercise signals skeletal muscle cells to increase mitochondria has been a question of interest for decades to many exercise scientists, including the applicant. Decreases in mitochondria occur in skeletal muscles of non-insulin dependent diabetes mellitus, obese, elderly, and physically inactive individuals and contribute to a reduced endurance to work in these populations. We recently found that muscles with a high mitochondrial content have little protein interaction with the 3'- untranslated region (UTR) of cytochrome c mRNA, compared to muscles with a low mitochondrial concentration. We also recently found a decreased RNA-protein interaction in muscles that were stimulated to increase cytochrome c mRNA. We believe this RNA-protein interaction is important for cytochrome c expression. The purposes of this proposal are to further characterize the structural and functional basis of the RNA-protein interaction and isolate the trans-proteins responsible for the regulation of cytochrome c gene. Specific aim 1 is to determine the sequence and structural basis for RNA-protein interaction is a 50-nucleotide (nt) region of the 3'-UTR of cytochrome c mRNA. A putative stem-loop structure, within which a 13-nt sequence was found to be conserved in the 3'-UTRs of rat, murine, human and chicken cytochrome c genes, was previously predicted by computer analysis within the 50-nt protein binding region. Specific aim 2 is to determine the function of RNA-protein interaction in the 3'-UTR of cytochrome c mRNA on its expression. Increased contractile activity could enhance cytochrome c gene expression by mRNA stabilization (which could be determined by measurement of its decay), or by translation acceleration (which could be determined by in vitro transcription and translation system). Specific aim 3 is to isolate and characterize the protein(s) binding to the 3'-UTR of cytochrome c mRNA. This information will provide information for identification of the signal that initiates cytochrome c adaptation to aerobic training. This proposal will contribute to an understanding of signaling mechanisms between exercise and mitochondrial biogenesis.